For many uses, in particular in the electronics industry, it is desirable to have safety fuses of the miniature or subminiature type (commonly consisting of a generally cylindrical housing provided with two metal end caps, between which a fuse link is secured), which are provided with leads connected to the end caps.
Hitherto two different methods have been used in practice for securing such so-called pig-tails to safety fuses. The first method consists of using additional end caps previously provided with a pig-tail, for example, by welding. Such caps already provided with a lead are pressed onto the end caps of the completed safety fuse. The interior dimensions of the additional end cap should be such that the end cap closely fits the end cap of the safety fuse. One disadvantage of this method is that an additional end cap, and hence more material, is required, while further dimensions of the parts concerned should be accurately controlled to prevent the additional end cap from becoming detached from the safety fuse end cap in operation.
Another method at present being employed is the use, during the manufacture of a safety fuse, of end caps already provided with a pig-tail, for example, by welding. However, an automatic production process for the manufacture of safety fuses using end caps already provided with a pig-tail is inconvenient because the pig-tails normally obstruct the handling of the fuse parts during assembly; at any rate it presents problems which do not occur when flat end caps are used during fuse assembly.
To avoid the problems encountered in the prior methods, it has already been considered to secure leads to completed safety fuses by welding such leads directly to the end caps of an otherwise completed safety fuse. Welding leads to an end cap of a safety fuse, however, is difficult, as welding gives rise to locally high temperatures also on the inside of the end cap. As a result, the solder on the inside will locally melt and evaporate, owing to which the fuse element or fuse link is apt to become detached from the end cap. It is even possible that owing to the local excessive heating, the solder explodes, as it were, and is thus blown far into the housing of the safety fuse. End caps for safety fuses are commonly made of nickel-plated brass, which nickel is commonly applied galvanically. Such end caps are of good quality and cheap. It is, however, very difficult, if not impossible, to produce a reliable connection between a lead and such an end cap by means of welding. This problem is additional to the above impossibility of welding to a completed safety fuse. The problem last mentioned can only be solved by selecting end caps of silver-plated copper, unplated copper and other materials. Such end caps are indeed used in the above methods of making safety fuses with pig-tails.
It is an object of the present invention to provide a method by which socalled pig-tails can be attached to the end caps of completed safety fuses without the occurrence of any of the problems mentioned hereinbefore and without any limitation in the choice of the material of the end cap.